1. Field of the Invention
The invention pertains generally to systems accomplishing motion control through servo mechanisms and, in particular, to systems requiring intensive signal processing such as those having multiple servo loops operating simultaneously.
2. Related Art
Digital signal processors have found use in servo control loop applications. Such micro processors are used to accomplish system management, to control parameter sampling, to execute servo position and tracking control, to perform complex calculations required for various control functions and to perform other related tasks. For example, Hasegawa, et al in "Fast Access Control of the Head Positioning Using A Digital Signal Processor" SPIE Vol. 1248, Storage Retrieval Systems and Applications (1990) p. 104, discloses the use of a digital signal processor for positioning the head of a storage and retrieval system. In conventional systems it has been necessary to multitask several servo loops through a single signal processor using, for example, complex priority-based interrupt schemes. For example, a calculation routine could be interrupted to permit servicing of a higher priority control device. As a result, multiple, concurrent complex signal processing and imbedded control functions have been difficult to implement.
In particular, servo requirements of high performance optical discs are among the more difficult of any storage system. Such optical discs require a number of complex control mechanisms. These include mechanisms for system management, control of a focus servo, and control of servos used for coarse and fine track positioning. In addition, it is necessary to provide control for a read and write laser power servo, spindle rotation control, field magnet control, and the ability to execute complex algorithms, such as seek algorithms. Such a magneto optic servo system requires high time precision and value precision analog sampling, fast servo calculation time and the flexibility to control several loops simultaneously, while allowing a wide dynamic range of adjustment of the parameters of the several servo loops.
Conventional approaches which multi-task several servo loops through a digital signal processor become bogged down in tedious real-time scheduling constraints. As performance requirements on such systems become more stringent, the need to improve the capability of the digital signal processing becomes apparent. This applies generally to all servo control loops and is not merely limited to the requirements of optical disc storage and retrieval systems.